Fluorocarbon based fluids have found widespread use in industry in a number of applications, including as refrigerants, aerosol propellants, blowing agents, heat transfer media, and gaseous dielectrics. Because of the suspected environmental problems associated with the use of some of these fluids, including the relatively high global warming potentials associated therewith, it is desirable to use fluids having the lowest possible greenhouse warming potential in addition to zero ozone depletion potential. Thus there is considerable interest in developing environmentally friendlier materials for the applications mentioned above.
Tetrafluoropropenes, having zero ozone depletion and low global warming potential, have been identified as potentially filling this need. However, the toxicity, boiling point, and other physical properties in this class of chemicals vary greatly from isomer to isomer. One tetrafluoropropene having valuable properties is 2,3,3,3-tetrafluoropropene (HFO-1234yf). Thus, there is a need for new manufacturing processes for the production of tetrafluoropropenes and in particular 2,3,3,3-tetrafluoropropene.
U.S. Patent Pub. No. 2010-0036179 discloses a process to manufacture 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) by reacting 2-chloro-3,3,3,-trifluoropropene (HCFO-1233xf) with hydrogen fluoride, in a liquid phase reaction in the presence of hydrogen chloride and a liquid phase fluorination catalyst. The hydrogen chloride is added into the reaction from an external source at a pressure of about 100 psig or more.
HCFC-244bb is an intermediate in the production of 2,3,3,3-tetrafluoropropene (HFO-1234yf) which is well known in the art as described in U.S. Patent Publication Nos. 2007-0007488 and 2007-0197842. HFO-1234yf has been disclosed to be an effective refrigerant, heat transfer medium, propellant, foaming agent, blowing agent, gaseous dielectric, sterilant carrier, polymerization medium, particulate removal fluid, carrier fluid, buffing abrasive agent, displacement drying agent and power cycle working fluid.
U.S. Patent Pub. No. 2009-0240090 discloses a process of making HFO-1234yf starting with chlorinated hydrocarbons. The process has three-steps. The first step involves fluorination of tetrachloropropene or pentachloropropane with HF to produce HCFO-1233xf. The second step involves hydrofluorination of HCFO-1233xf with HF to produce HFC-244bb. The conversion of HCFO-1233xf is not complete. Some of unreacted HCFO-1233xf is recycled back into the second step hydrofluorination reactor, but some of HCFO-1223xf is carried forward into the third step dehydro-chlorination reactor. The third and final step involves dehydrochlorination of HFC-244bb to produce HFO-1234yf product. Again, conversion of HCFC-244bb is not complete. Unreacted HCFO-244bb and HCFO-1233xf carried from the third step reactor is recycled back to the second step reactor. The presence of HCFO-1233xf in the third step reactor feed does not allow recycle of unreacted HCFC-244bb to the third step reactor. This results in larger size (lower capacity) of the second step reactor. Also, recycle of HCFC-244bb back into the second step hydrofluorination reactor may result in the formation of over fluorinated by-products such as 1,1,1,2,2-pentafluoropropane (HFC-245cb) and increased HF consumption.
It would be preferred to remove HCFO-1233xf and other halogenated olefins impurities produced in the first two process steps from the HCFC-244bb intermediate product prior to sending the feed into the dehydrochlorination reactor to produce final product HFO-1234yf. This would allow recycle of unreacted HCFC-244bb back to the third step reactor minimizing the yield loss.
HCFC-244bb and HCFO-1233xf are inseparable using conventional separation techniques known in the art since HCFC-244bb and HCFO-1233xf form a binary azeotrope or azeotrope-like composition which is described in U.S. Pat. No. 7,803,283. It has been found that HCFO-1233xf (and other halogenated olefin impurities) can be separated from HCFC-244bb using a solid adsorbent such as activated carbon or other solid adsorbents having similar properties.
When it is desired to separate halogenated olefin impurities including HCFO-1233xf from HCFC-244bb, the mixture of halogenated olefin impurities including HCFO-1233xf and HCFC-244bb can passed over solid adsorbent that preferentially adsorbs halogenated olefin impurities including HCFO-1233xf and then the two compounds can be separated. Essentially pure HCFC-244bb and HCFO-1233xf together with other halogenated olefin impurities can be recovered. Then essentially pure HCFC-244bb can be fed into the dehydrochlorination reactor where it is converted to HFO-1234yf. After separating unreacted HCFC-244bb from HFO-1234yf product, HCFC-244bb exiting dehydrochlorination reactor can be recycled back into the reactor to increase the yields of the final product HFO-1234yf.